In the valve art it is known to provide a vertically slidable gate, operable by a turn wheel to open and close the flow passage and to provide a pressure relief valve on the suction side of the gate as in U.S. Pat. No. 4,050,857 to Paul A. Leach of Sept. 27, 1977.
There is also on the market a valve with a horizontally slidable piston advanced and retracted by a turn wheel to open and close the flow passage, the pressure relief valve being mounted on an elbow and operating whether the valve is open or closed. This valve is a product of Fire Products Division of Snap-Tite, Inc., Union City, Pa. 16438.
A valve having no pressure relief system but having a spherical hollow core cooperating with an annual, bevelled valve seat, the core turned by a turn wheel to open and close the valve flow passage, is disclosed in U.S. Pat. No. 2,690,894 to Blevans of Oct. 5, 1954.